Variable capacitor including a rotatable dielectric disc

ABSTRACT

A variable capacitor forming part of an attenuator section includes a rotatable ceramic disc having a metalized configuration on its upper side which may be mutually juxtaposed with respect to a pair of metalized portions on a ceramic substrate therebelow. The metalized ceramic disc is superimposed by a rotatable plastic body engageable for rotating the disc and having an extension depending through an aperture in the substrate to provide an axis portion for the combined rotatable member. A spring is interposed between a grounded metal cover and a portion of the plastic body, urging the ceramic disc toward the substrate.

United States Patent Wilhoit VARIABLE CAPACITOR INCLUDING A ROTATABLEDIELECTRIC DISC [52] US. Cl. ..317/249 R, 317/253, 317/249 D, 323/74,323/93, 333/81 R [51] Int. Cl. ..H0lg 5/06, H03h 7/24 [58] Field ofSearch.....333/81 R; 323/63, 74, 77, 93; 317/253, 249 R, 249 D [56]References Cited UNITED STATES PATENTS 3,310,760 Swan ..317/253 X [1513,693,058 51 Sept. 19,1972

3,225,275 12/1965 Uchida ..317/249 D 3,588,642 6/1971 Fabricius..317/249 D 3,287,613 11/1966 Devins ..317/249 D 3,426,267' 2/ 1969Weller ..323/93 X 3,105,922 10/1963 Fukui et a1 ..323/74 X PrimaryExaminer--Paul L. Gensler Attorney-Buckhorn, Blore, Klarquist & Sparkman[5 7] ABSTRACT A variable capacitor forming part of an attenuatorsection includes a rotatable ceramic disc having a metalizedconfiguration on its upper side which may be mutually juxtaposed withrespect to a pair of metalized portions on a ceramic substratetherebelow. The metalized ceramic disc is superimposed by a rotatableplastic body engageable for rotating the disc and having an extensiondepending through an aperture in the substrate to provide an axisportion for the combined rotatable member. A spring is interposedbetween a grounded metal cover and a portion of the plastic body, urgingthe ceramic disc toward the substrate.

5 Claims, 11 Drawing figures VARIABLE CAPACITOR INCLUDING A ROTATABLEDIELECTRIC DISC CROSS-REFERENCE TO RELATED APPLICATION This applicationis a continuation-in-part of my application Ser. No. 830,071, filed June3, 1969, now U.S. Pat. No. 3,622,919, entitled Step Attenuator of LowInductance and High Bandwidth which is assigned to the assignee of thepresent invention.

BACKGROUND OF THE INVENTION Use of variable capacitors is frequentlydesired in tuning circuits,.attenuation circuits, and the like, butoften tend to be complex in construction, rendering the same difficultto realize in miniature applications. For example, since a variablecapacitor conventionally has a movable plate means of some kind, acontact must ordinarily be provided for making a continuois connectionto such movable plate means. While fairly heavy bearings can make asuitable connection in the case of fairly large sized variablecapacitors, a small frictional contact may suffice in a miniaturizedversion, leading to a high resistance connection and contact noise.Alternatively, a permanent connection may be made which is subject toflexing failure.

SUMMARY OF THE INVENTION According to the present invention,v a variablecapacitor device comprises a fixed member and a movable member whereinthe fixed member is provided with a pair of conducting layers formingfixed plates of the capacitor. The movable member has a conducting layerfor providing a second or variable plate of the capacitor, with thismovable member layer having a configuration for variable mutualjuxtaposition with the fixed member conducting layers as the movablemember is rotated with respect to the fixed member. Means makeelectrical connection with each of the pair of fixed member layers whilethe movable members conductive layer is electrically floating. Avariable capacitance is thereby provided as between the fixed memberlayers, without necessity for connection to the movable member layer.

The capacitor device according to the present invention advantageouslyforms part of a miniaturized attenuator section of the type set forth inmy above-mentioned application, rendering the use of a large number ofsuch attenuator sections more efficacious in an attenuation selectionsystem.

It is an object of the present invention to provide an improved variablecapacitor device having no frictional or other electrical connectionsbetween variable and fixed parts.

It is another object of the present invention to pro vide an improvedvariable capacitor device adaptable for miniaturized construction andwhich does not introduce moving contact noise or the like.

It is another object of the present invention to provide an improvedvariable capacitor device characterized by long and dependable operationin a miniaturized construction, despite the presence of moving parts.

It is another object of the present invention to provide an improvedattenuator section adapted for miniaturized construction which isdependable in operation and which includes a variable capacitor meansadjustment.

It is a further object of the present invention to provide an improvedvariable capacitor means which is simple and economical in construction,and dependable in operation.

The subject matter which I regard as my invention is particularlypointed out and distinctly claimed in the concluding portion of thisspecification. The invention, however, both as to organization andmethod of operation, together with further advantages and objectsthereof, may best be understood by reference to the followingdescription taken in connection with the accompanying drawings whereinlike reference characters refer to like elements.

DRAWINGS FIG. 1 is a plan view of an attenuator section according to thepresent invention;

FIG. 2 is a side elevational view of the FIG. 1 attenuator section withparts thereof broken away and illustrating the construction of variablecapacitor devices according to the present invention;

FIG. 3 is a partially schematic view showing the relative positions ofelectrical components and ground contact points in the aforementionedattenuator section;

FIG. 4 is a more fully schematic diagram of the electrical circuit ofthe above-mentioned attenuator section;

FIG. 5 is a top view of a ceramic substrate forming part of theattenuator section and variable capacitor devices according to thepresent invention;

FIG. 6 is a bottom view of the FIG. 5 ceramic substrate;

FIG. 7 is a top view of a ceramic disc forming part of a capacitordevice according to the present invention;

F IG. 8 is an edge view of the FIG. 7 disc;

FIG. 9 is a side view of an insulating body for providing means formounting the FIG. 7 disc for rotational motion, and engaging means forbringing about such rotation;

FIG. 10 is a top view of the FIG. 9 body; and

FIG. 11 is a combined movable member according to the present inventionincluding the FIG. 7 disc and the body of FIG. 9 for rotating the same.

DETAILED DESCRIPTION Referring to FIGS. 1 through 4, illustrating acapacitor device according to the present invention and an attenuatorsection including the same, such attenuator section comprises a ceramicstrip or substrate 10 which is soldered or otherwise bonded to. agrounded metal clip member or cover 12. A pair of voltage dividerresistors 14 and 16, connected in series between an input contact 18 andgrounded cover 12, are formed of resistance material on the bottom ofthe ceramic strip. The common terminal of such voltage divider isconnected to an output contact 20. Both of the contacts 18 and 20 areinsulatingly mounted on the metal cover by sleeves 22, suitably formedof plastic material, through which shafts of the contacts extend to theceramic substrate 10 where connections are made from the contact shaftsto circuitry on the bottom of the substrate.

The resistive coatings forming resistors 14 and 16 are more particularlyillustrated in FIG. 6 wherein the coatthe substrate providing conductorsforming a fixed part of capacitor 24. A partially metalized ceramic disc26 forms a movable member of capacitor 24, such disc being rotatable bya slotted adjustment member or body 28 secured to the disc. Body 28 isbiased for urging disc 26 toward substrate 10 by a spring 40 disposedbetween a shoulder 42 of body 28 and the underside of cover 12. Body 28suitably extends through a coaxial aperture in cover 12 and isconveniently provided on its upper end with a diametrically extendingslot 43 engageable with a screwdriver or the like by means of which body28, and consequently disc 26, may be rotated.

The input capacitor 24 is connected between input contact 18 andgrounded cover 12. A variable coupling capacitor 30 is also formedintegrally with .the ceramic substrate and is connected between inputcontact 18 and one terminal of a damping resistor 32. The dampingresistor is provided as a resistive coating on the top of the ceramicsubstrate 10, as illustrated in FIG. 5, and has its other terminalconnected to output contact 20 at the common junction of the voltagedivider resistors. The damping resistor prevents ringing by dampingsignal oscillations without materially attenuating the signaltransmitted through the voltage divider resistors. Such a dampingresistor typically has a value much lower in resistance than that of thevoltage divider resistors. As is well understood by those skilled in theart, the voltage divider resistors will have different values dependentupon the attenuation desired.

A shunt capacitor 34 may be employed in the at tenuator section, and isconnected between ground and the common terminal of coupling capacitorand damping resistor 32. Two grounding fingers 35, extending from thesides of cover 12, connect the capacitor 34 to ground. The capacitors 30and 34 provide an AC voltage divider while resistors 14 and 16 provide aDC voltage divider for the signal being attenuated. The capacitors willhave values selected for maintaining proper circuit constants as wellunderstood by those skilled in the art. Input capacitor 24 is adjustedto provide each attenuator section with the same input capacitance andcompensates for the changes in the values of capacitors 30 and 34 withchanging attenuation, as well as for other capacitance which may bepresent.

A plurality of attenuator sections as described herein are mountedperipherally on a drum in the attenuator apparatus according to theaforementioned application, such that the attenuator sections areindividually selectable with rotation of the drum, different of theattenuators providing differing attenuation. An attenuator section isconnected when its input and output contacts l8 and 20 meetfixedcontacts, not shown herein. Four ground contacts'36 engage themetal cover 12 for grounding the same in a manner achieving lowinductance and a wide bandwidth as further set forth in the abovereferenced application. The attenuator sections are mounted within slotsin the aforementioned drum, with side flanges 38 engaging portions ofsuch drum.

According to a feature of the present invention, capacitors 24 and 30are constructed such that no connection is made to the metalized ceramicdisc 26, but rather the same is electrically floating, while beingadapted for variable capacitive relation with metalized portions onceramic substrate 10. A moving contact is eliminated, with attendantproblems related to maintaining a low resistance connection, and noiserelated to movement of such contact. Referring particularly to FIG. 7,illustrating the planar ceramic disc 26 forming a movable member of acapacitor in accordance with the present invention, this disc hasadhered thereto a pair of flat surfaced conductors 44 in the form ofmetalized portions or conductive coatings, suitably substantiallysemicircular in configuration, being insulated from one another, andeach lying on one side of a central aperture 46 in disc 26. Theconductive coating or coatings form movable capacitor plates. Althoughtwo such flat surfaced conductors are illustrated, one of the conductiveconfigurations 44v is sufficient for providing the desired capacitancein instances where the attenuation constants indicate a smallercapacitance is suitable. Metalized coating is applied to the ceramicdisc in a conventional manner.

A fixed member of the variable capacitor according to the presentinvention is provided by the ceramic substrate 10 upon which aredisposed metalized portions or conductive coatings forming flat surfacedconductors for juxtaposition with the coating on disc 26. These coatingsprovide fixed capacitor plates. Referring to FIG. 5, for example, a pairof flat surfaced conductors for capacitor 24, disposed in the same planeon substrate 10, are numbered 48 and 50. A first metal coating 48provides a flat surfaced conductor disposed at one end of ceramicsubstrate 10 on the upper side thereof and makes connection with adepending portion of metal cover 12 by means of soldering. The firstmetal coating 48 is entirely on one side of an aperture 52 which isslightly larger than aperture 46 in disc 26. On the opposite side ofaperture 52, a metal coating 50, insulated from coating 48 by thesubstrate, provides a second flat surfaced conductor for the fixedcapacitor member. Conductor 50 is here substantially semicircular inconfiguration and suitably matches one of the metal coatings 44 on disc26. It also forms an integral part of metalized conductor 54 extendingalong the upper surface of substrate 10 for making connection withterminal 18, the shaft of which will extend through aperture 56 wherethe two may be soldered together.

To provide the desired capacitive relation, disc 26 is disposed abovesubstrate 10 with aperture 46 aligned with aperture 52, and with themetal coating 44 on disc 26 disposed upward or away from coatings 48 and50.

Thus, disc 26 provides insulated spacing for the capacitor. It will beseen that if one of the metal coatings 44 is substantially entirelyjuxtaposed with respect to coating 48, while the other coating 44 issubstantially juxtaposed with respect to'coating 50, capacitor 24 willprovide minimum capacitance as between coatings 48 and 50. If, however,disc 26 is rotated by 90 in either direction, a substantially maximumcapacitance is achieved, wherein coatings 44 provide a bridgetherebetween. Any degree of capacitive adjustment between the twoextremes can be provided without need of making connection to theconductive coating or the coatings on the movable element. Thecapacitance range can be changed by selection of a differing thicknessfor disc 26, enlarging or contracting the size of the disc and/or theconductive layer, placing one or both of the fixed coatings on theopposite side of the substrate, or the like.

Further considering FIGS. 9 through 11, these figures illustrate meansfor mounting the disc 26 for rotational motion with respect to the fixedmember, and means for engaging the same for rotation, in the form ofplastic body 28, is suitably adhered to the top surface of disc 26. Body28 is desirably adhered to ceramic disc 26 over the conductive layer orlayers 44. The body 28, which is suitably formed of an insulatingplastic material having a low dielectric constant, and having rigidmechanical characteristics, extends through central aperture 46 in disc26 to provide a lower axis portion 58 for the movable member. This axisportion has an outside diameter adapted to be received in bearingrelation through aperture 52 in sub strate 10. Plastic body 28 isillustrated by itself in FIGS. 9 and 10, and is illustrated as securedto disc 26 in FIG. 1 l. The body 28 includes a lower cylindrical portion60 having a diameter substantially matching that of disc 26, and anupper smaller diameter portion 62 provided with the engageable slot 43by means of which the body is turned for varying the capacitance.Therebetween, body 28 is provided with a shoulder 64 of intermediatediameter, around which spring 40 is received for bearing upon the lowerportion 60 as illustrated in FIG. 2

which shows the assembled capacitor. The capacitor plate spacing ismaintained by the spring bias thus applied. The body 28 and disc 26 areadhered by conventional methods so as to form a substantially unitarymember.

Referring to FIG. 5, conductive layer 54 to the right of aperture 56terminates in a first flat surfaced conductor 66 of capacitor 30, whilea second, coplanar, flat surfaced conductor 68 is provided by part of asimilar metal coating 70, insulated from the first, and extending to theright for making connection with the resistive coating which formsresistor 32. Resistor 32 is located between coating 70 and metalizedland 72 adapted for connection by means of soldering to the shaft ofoutput terminal 20.

Capacitor 30 is further provided with a central aperture 74 in substrate10 adapted to receive the axis portion 58 of a capacitor movable memberas illustrated in FIGS. 9 through 11. It will be observed that each ofthe flat surfaced conductors 66 and 68 are quarter-circular in thisinstance, and consequently a ceramic disc 26 forming part of the movablemember need have only one conductive coating 44 applied thereto foraligned juxtaposition with metal coatings 66 and 68, in the maximumcapacity position of the capacitor. In this connection, it should benoted the fixed conductor configurations illustrated herein forcapacitors 24 and 30 are only two alternatives, with other variations inconfi uration bein ossible for rovid'n re uisit low arid high capa itnce conditi ns of r naxi inizec? and minimized mutual juxtaposition ofthe fixed and movable conductor surfaces.

While I have shown and described preferred embodiments of my invention,it will be apparent to those skilled in the art that many changes andmodifications may be made without departing from my invention in itsbroader aspects. I therefore intend the appended claims to cover allsuch changes and modifications as fall within the true spirit and scopeof my invention.

I claim:

1. A variable capacitor device comprising:

a fixed capacitive member including an insulating substrate with a firstpair of conducting layers adhered thereon;

a movable capacitive member including a disc of insulating materialhaving a second pair of conducting layers adhered thereon;

means for axially mounting said movable member for rotation with respectto said fixed member so that said disc provides spacing between saidfirst pair of conducting layers and said second pair of conductinglayers;

engaging means for bringing about said rotation including an insulatingbody movable with said disc and extending through the center of saiddisc to provide an axis portion for said movable member and forming partof the means for mounting said movable member for rotation, said bodyhaving an engagable portion for rotating the same;

means for urging said fixed and movable capacitive members toward oneanother during rotational movement of said movable member;

said second pair of conducting layers having configurations adaptablefor variable juxtaposition above said fixed member so that the movablemember provides variable capacitive coupling between said first pair ofconducting layers during said rotational movement.

2. The device according to claim 1 wherein the adhered conducting layerson said disc are substantially semicircular.

3. The device according to claim 1 further including a cover having anaperture providing access to said body substantially coaxial with saidaxis portion,

said means for urging said members together comprising a spring disposedbetween said cover and a shoulder provided on said insulating body abovethe conductor adhered to the movable member.

4. The device according to claim 1 wherein said fixed member is providedwith an aperture for receiving the axis portion provided by said body,and further forming part of said means for mounting said movable memberfor rotational motion.

5. The device according to claim 1 wherein said body is formed ofplastic.

1. A variable capacitor device comprising: a fixed capacitive memberincluding an insulating substrate with a first pair of conducting layersadhered thereon; a movable capacitive member including a disc ofinsulating material having a second pair of conducting layers adheredthereon; means for axially mounting said movable member for rotationwith respect to said fixed member so that said disc provides spacingbetween said first pair of conducting layers and said second pair ofconducting layers; engaging means for bringing about said rotationincluding an insulating body movable with said disc and extendingthrough the center of said disc to provide an axis portion for saidmovable member and forming part of the means for mounting said movablemember for rotation, said body having an engagable portion for rotatingthe same; means for urging said fixed and movable capacitive memberstoward one another during rotational movement of said movable member;said second pair of conducting layers having configurations adaptablefor variable juxtaposition above said fixed member so that the movablemember provides variable capacitive coupling between said first pair ofconducting layers during said rotational movement.
 2. The deviceaccording to claim 1 wherein the adhered conducting layers on said discare substantially semicircular.
 3. The device according to claim 1further including a cover having an aperture providing access to saidbody substantially coaxial with said axis portion, said means for urgingsaid members together comprising a spring disposed between said coverand a shoulder provided on said insulating body above the conductoradhered to the movable member.
 4. The device according to claim 1wherein said fixed member is provided with an aperture for receiving theaxis portion provided By said body, and further forming part of saidmeans for mounting said movable member for rotational motion.
 5. Thedevice according to claim 1 wherein said body is formed of plastic.